Small, usually matted herbs growing in rapids and waterfalls, flowering when the water subsides seasonally, very variable in size, the smaller ones thalloid and closely adhering to the supporting rocks, the larger ones with distinct stems often arising in pairs from long and thin roots, in other instances rootless; sterile plants often larger and coarser than the fertile ones. Leaves alternate, di- or tristichous, in the stemless species sometimes united at the base and springing in 2 rows from an irregular base, entire or much divided, sometimes with bundles of minute threads on one or both sides; stipule 1, a sheath and a ligula sometimes present. Flowers solitary or fascicled between the leaf-bases or at the ends of short branches .or in distinct inflorescences, hermaphrodite, actinomorphic or zygomorphic, the younger ones enveloped by a thin spathe or by a few leaves. Tepals 2 to many, distinct or reduced to minute scales, free or united. Stamens 1 to many, alternate with the tepals in a complete or incomplete whorl, free or united to the tepals; anthers sagittate, 4-celled, dehiscing by 2 longitudinal slits, introrse or extrorse, dorsi- or basifixed; pollen 1- or 2-celled. Ovary superior, sometimes oblique or nearly perpendicular to the (frequently) distally enlarged pedicel, 2- or 3-, or sometimes 1-celled; carpels equal or unequal, ribbed or smooth without, the placenta. axile, fleshy, with 2 to numerous anatropous ovules; ovules with 2 in- teguments; styles 2-3, free or cohering, each with a distinct stigma. Fruit de- hiscing septifragal with 2 or 3 valves, in fruits with unequal cells the smallest valve sometimes soon falling off; seeds 2 to many, without endosperm.

Distribution

About 200 species distributed in the tropics throughout the world, ascending the southern Appalachian Mountains in the southeastern United States.